Most mowers today use elongate and generally rectangular cutting blades having a sharpened cutting edge at each end leading the direction of rotation of the blade which cuts the grass it contacts. Smaller mowers for residential use typically have a single deck which houses a single cutting blade with a side discharge chute through which cut grass is expelled. Commercial mowers are used on golf courses, cemeteries, and parks, and typically use a larger deck housing a longer blade. Many commercial mowers use two or three such decks ganged together such that the cutting blade of each deck is simultaneously driven by an internal combustion engine mounted to the frame of the mower. In some instances, each deck can be equipped with two or more cutting blades.
For safety reasons, federal law prohibits the speed of the outer tip of the rotating cutting blade from exceeding 19,000 feet per minute. For a mower moving at five miles per hour (440 feet per minute) using conventional rectangular cutting blades each having two cutting edges with one cutting edge disposed adjacent one end of the blade and the other cutting edge disposed adjacent the other end of the blade and rotating at a speed such that each blade tip is moving at a velocity of about 19,000 feet per minute, the following analysis applies:
30 inch blade
2021 R.P.M.=4043 cuts/minute=1.306" cut per blade revolution PA0 2878 R.P.M.=5757 cuts/minute=0.917" cut per blade revolution PA0 4043 R.P.M.=8085 cuts/minute=0.653" cut per blade revolution PA0 6129 R.P.M.=12,258 cuts/minute=0.431" cut per blade revolution
21 inch blade
15 inch blade
10 inch blade
In general, it is desirable to take smaller bites or cuts per blade revolution because it results in a better quality cut and result in smaller pieces of cut grass which are easier to discharge and lessen clogging.
However, rectangular cutting blades possess less material resulting in less inertia requiring more horsepower to maintain their speed of rotation at the desired. Moreover, since they have only two cutting edges, they must take larger bites or cuts per blade revolution. Quite often, because the effective cutting region of the blade is much smaller than the actual length of the cutting edge, blade wear occurs much more rapidly at the tips where cutting is taking place. As a result of all of these factors, the cutting efficiency of conventional rectangular blades is less than optimum and blade wear along the blade's effective cutting region rapidly reduces during operation.
As a result of lower blade efficiency and increased wear, the quality of cut is significantly less than desired. More particularly, the grass is not cleanly cut and is often frayed or ragged. This poor cut damages the grass causing its cut tips to turn brown in less than a few days. This premature and unnecessary browning of the grass is particularly undesirable on golf courses and cemeteries where appearance is important. Moreover, for golf courses, a precise and uniform cut is highly desired so that golf balls roll uniformly on all of the fairways of the course.
To better nourish the grass, mulching or recirculating mowers are in favor. Most, if not virtually all mulching mowers utilize a deck that lacks any discharge chute for capturing the cut grass clippings within the deck. In mulching, it is desirable to cut the grass clippings into as small of pieces as possible so they will fall between the uncut grass blades to the ground to avoid messy clumps of clippings from accumulating on top of the grass. Additionally, smaller grass clippings are more desirable because they degrade more quickly returning nutrients to the ground more rapidly.
Unfortunately, mulching mowers often lack sufficient suction to keep cut grass clippings suspended within the deck long enough to be recut into sufficiently small pieces.
Moreover, cut clippings disposed near the rear of the deck can fall to the ground after only being cut once reducing their efficiency as mulch because the clippings are so large.
Many commercial and home mowers of the tractor and/or triplex variety have two front wheels, two rear wheels and are of front wheel drive and rear wheel steer construction for better maneuverability. Unfortunately, such tractor-type mowers possess less traction and are thus less suitable for mowing grass on hills and other types of uneven terrain, such as what is commonly found on golf courses.
Traditionally, triplex mowers have been used in many forms for many years, but only with reel mowers. These are large acreage commercial mowers that use three cutting decks with each deck being from four to six feet long. Each deck has two or three rectangular cutting blades each of which typically is twenty to twenty four inches long. Unfortunately, because these decks are so large and particularly because they are so long, they can cause scalping and an uneven cut particularly when mowing uneven, rough or hilly terrain.
What is needed is a mower which uses a more efficient cutting blade for producing a better quality cut while increasing cutting efficiency and minimizing horsepower demands upon the internal combustion engine driving the mower. What is needed is a cutting blade offering more than two cutting edges to decrease the length of grass cut per blade revolution for increasing cut quality. What is also needed is a cutting blade of aerodynamic construction that lessens the power required to rotate it at a desired rotational speed. What is also needed is a cutting blade having greater inertia for being able to encounter cutting obstacles and still maintain cut quality. What is also needed is a mulching or recirculating mower deck which discharges cut grass clippings forwardly to better ensure the cut clippings are recut into smaller clippings to produce better mulch. What is further needed is a mower of tractor-type construction having improved traction and stability for enabling the mower to better maneuver and more uniformly cut grass on uneven and hilly terrain. What is still further needed is a commercial triplex mower which uses smaller cutting blades and cutting decks that float along the terrain to minimize scalping and uneven cutting.